The prior method of manufacturing pressure vessels from tubing involved the process of first wrapping a length of tubing around a solid mandrel forming a number of continuous coils, then allowing the coils to relax so they could be removed from the mandrel. The coiled tube was then remounted on a mandrel with a larger diameter and a welder with a seam tracking device was used to weld the coils together to provide the continuous cylindrical wall for the pressure vessel.
Although the above described process produced the pressure vessel circular wall from tubing, it was difficult to maintain a consistent level of quality required for the circular wall which had to be strong and leak free. When the wrapped coils were removed from the mandrel prior to welding, it was quite difficult to get the adjacent coils to stay in contact with each other to provide the proper environment for the welding of the coils together. Hence a poor quality of weld and joint were produced which would either leak or be weakened by burning too deep into the tubing wall.
The two step operation was time consuming and the seam tracking welding equipment was quite expensive resulting in a rather costly process that was difficult to control.
The present invention is directed to overcoming the problems as set forth above.